i) Field of the Invention
The present invention relates to a control system for a linear synchronous motor vehicle, and more particularly to a speed electromotive force phase control system adapted to low speed.
ii) Description of Related Art
A known example of conventional control systems for a linear synchronous motor (hereinafter referred to as xe2x80x9cLSMxe2x80x9d) vehicle comprises, as shown in FIG. 7, a propulsion coil 61 provided along a guideway on a ground; a field coil 62a provided on a vehicle 62 so as to face the propulsion coil 61; a speed controller 63 for outputting a current command value I* computed by proportional-integral operation of the deviation between a speed command value v* and the actual speed v; a converter controller 64 for performing proportional-integral operation of the deviation between the current command value I* and a coil current I flowing through the propulsion coil 61 and outputting a voltage command value V* with a sine wave in synchronism with a position detecting phase xcex8p as a phase reference to indicate the position of the vehicle; a power converter 65 for outputting a three-phase output voltage V in accordance with the voltage command value V* to the propulsion coil 61 through a feeder 66; a current detector 67 for detecting the coil current I flowing through the propulsion coil 61; a cross induction line 68a arranged along the track so as to obtain information about the vehicle position; a position detector 68 for detecting a relative position of the field coil 62a to the propulsion coil 61 based on a signal generated in the cross induction line 68a and outputting the position detecting phase xcex8p; and a speed detector 69 for performing operation of an actual speed v necessary for speed control from the position-detecting phase xcex8p and outputting the actual speed.
The propulsion coil 61, particularly as shown in FIG. 8A, is composed of coil sections, such as 71A1, 71B1, and 71C1 having a prescribed length and a plurality of groups of coils for propulsion therein, which are arranged on both sides of the vehicle 62 such that respective coil sections on one side are shifted by half of their length relative to respective coil sections on the other side. As shown in FIG. 8B, each coil section comprises a plurality of groups of coils for propulsion of three phases, i.e. U-phase, V-phase, and W-phase, respectively, which groups are arranged along the forward direction of the vehicle. By supplying three-phase alternating current to these groups of coils, shifting magnetic field is generated. A phase reference is predetermined by using the length of a group of coils for propulsion of 2.7 m as one cycle (360xc2x0) of an electrical angle, and information about the vehicle position is obtained by detecting the phase reference with the position detector 68.
The feeder 66 for supplying electricity, or outputting output voltage V, from the power converter 65 to each coil section consists of three feeder cables corresponding to three inverters 65A, 65B, and 65C, respectively, contained in the power converter 65. By controlling feeder section switches such as 72A1, 72B172C1 . . . (omitted in FIG. 7) separately, electricity is supplied only to the three lines of coil sections in the vicinity of the running vehicle 62.
For example, when the vehicle 62 runs in the right direction as shown in FIG. 8A, three feeder section switches 72C1, 72A2, and 72B2 are closed and electricity is supplied to the coil section 71C1 through a C-line inverter 65C, to the coil section 71A2 through an A-line inverter 65A, and to the coil section 71B2 through a B-line inverter 65B, respectively. When the vehicle 62 reaches the position corresponding to the coil section 71B2, a feeder section switch 72C2 is closed while the feeder section switch 72C1 is opened, with the result that power supply is stopped for the coil section 71C1 and started for the coil section 71C2 instead.
An LSM vehicle is driven by propulsion force generated by the interaction between a magnetic field generated by the field coil 62a, which is a superconductive coil, and a magnetic field generated in the propulsion coil 61 due to the three-phase output voltage V outputted from the power converter 65. To control driving of the LSM vehicle, the position detecting phase xcex8p is inputted into the converter controller 64 as a phase reference indicating the position of the vehicle 62, and an actual speed v is computed by the speed detector 69 based on the position detecting phase xcex8p. Therefore, accurate detection of the position detecting phase xcex8p, i.e. the vehicle position, is required.
To fulfill this requirement, the cross induction line 68a is laid along the length of the track and a signal (an electric wave) is transmitted from the vehicle 62 to the cross induction line 68a. By processing a sine wave signal, which is generated in the cross induction line 68a due to the signal transmission from the vehicle 62, with the position detector 68, the position detecting phase xcex8p is obtained. Thus, substantially accurate position detection is achieved.
However, the above-described method of detecting the position of the vehicle 62 requires accurate laying of the cross induction line 68a along the length of the track and maintenance thereof as well. It leads to a large amount of labor and high cost for construction and maintenance of the vehicle position detecting system.
To solve this problem, a method of detecting the vehicle position without providing a ground installation such as the cross induction line 68a has been thought out. In this method, electromotive force induced in the propulsion coil 61 due to the running of the vehicle 62 (hereinafter referred to as xe2x80x9cspeed electromotive forcexe2x80x9d) is estimated, and a phase indicating the vehicle position (hereinafter referred to as xe2x80x9cspeed electromotive force phasexe2x80x9d) xcex8e is obtained based on the estimated value. Specifically, as shown in FIG. 9, three-phase/xcex1xcex2 converters 81a, 81b convert the output voltage V outputted from the power converter 65 and the coil current I flowing through the propulsion coil 61 to voltages Vxcex1, Vxcex2 and currents Ixcex1, Ixcex2, respectively, in xcex1-xcex2 coordinate system. A speed electromotive force observer 82 estimates the speed electromotive force from the voltages Vxcex1, Vxcex2, currents Ixcex1, Ixcex2, and a vehicle angular speed xcfx89, to obtain estimated speed electromotive force values Z xcex1, Zxcex2. Resistance R and inductance L peculiar to the coil sections located in the neighborhood of the running vehicle 62 are further inputted as control constants to the speed electromotive force observer 82, and then, speed electromotive force phase calculator 83 computes the speed electromotive force phase xcex8e by an equation (i) below.                               θ          ⁢                      xe2x80x83                    ⁢          e                =                              tan                          -              1                                ⁢                                    Z              ⁢                              xe2x80x83                            ⁢              β                                      Z              ⁢                              xe2x80x83                            ⁢              α                                                          (        i        )            
As described above, by computing the speed electromotive force phase xcex8e and using the same as the phase reference instead of the position detecting phase xcex8p, ground installations such as the cross induction line 68a and the position detector 68 become unnecessary. However, when the speed electromotive force phase xcex8e, obtained by estimating the speed electromotive force as shown in FIG. 9, is used as the phase reference, there is a problem that the stable speed electromotive force phase xcex8e cannot be obtained when the running speed of the vehicle is low (for example, the speed under 15 km/h).
Specifically, because the speed electromotive force phase xcex8e is directly calculated by the above equation (i), it is likely to be affected by the control constants such as the resistance R and the inductance L of the coil sections. In short, this method has no robust stability against changes of the control constants, and when these control constants change according to a transition of the coil sections located in the neighborhood of the running vehicle 62, a deviation between the speed electromotive force phase xcex8e and the actual vehicle position (phase reference) is apt to become substantial.
When the vehicle is running at high speed, the deviation is subtle and the speed electromotive force phase xcex8e is capable to be utilized. However, when the vehicle is running at low speed, the speed electromotive force gets small and the deviation in xcex8e grows large. As the deviation between the actual phase reference and the speed electromotive force phase xcex8e grows large, it is difficult to use xcex8e as the phase reference upon the drive control of the LSM vehicle.
Wherefore, a principal object of the present invention is to provide a control system for an LSM vehicle outputting to a propulsion coil a voltage corresponding to a voltage command value based on a current command value, a phase reference, etc., which overcomes the above mentioned problem and obtains the stable phase reference with a minimum deviation even when the vehicle is running at low speed.
This and other objects are accomplished with a speed electromotive force phase control system in a control system for an LSM vehicle driven by propulsion force obtained by an interaction between the magnetic field produced in a propulsion coil arranged along a guideway on a ground by an output voltage V outputted from a power converting means and a magnetic field produced by a field coil provided on the vehicle so as to face the propulsion coil, the speed electromotive force phase control system generating a phase reference xcex8 as a vehicle position signal when the vehicle is running under a predetermined speed.
In the control system for an LSM vehicle, a voltage command value is outputted by a conversion control means based on the current command value outputted from a speed control means, a coil current I flowing through the propulsion coil detected by a current detection means and a vehicle position signal in the same manner as in the above described conventional driving control system. According to the voltage command value, the output voltage V is outputted to the propulsion coil by the power converting means.
In this case, the phase reference xcex8 as a vehicle position signal with respect to the LSM including the field coil and the propulsion coil is the relative position of the field coil to the propulsion coil indicated in the form of an electrical angle. For example, in the case of the LSM in which a movable magnetic field is produced by supplying three-phase alternating current to the propulsion coil, the distance between a U-phase coil and the field coil in the running direction of the vehicle is indicated in the form of an electrical angle, which is used as the phase reference xcex8.
In the speed electromotive force phase control system according to the present invention, as shown in FIG. 1, firstly a dq conversion means 1 converts the output voltage V from the power converting means and the coil current I flowing through the propulsion coil to a d-axis voltage Vd, a q-axis voltage Vq, a d-axis current Id and a q-axis current Iq, respectively, in the dq rotary coordinate system. Then, based on the obtained voltages Vd, Vq, currents Id, Iq, and a vehicle angular speed xcfx89, a speed electromotive force estimation means 2 estimates speed electromotive force induced in the propulsion coil.
Such estimation can be made, for example, by the observer theory in the modern control theory, and in that case, resistance, inductance and the like of the propulsion coil are used as control constants in an observer. The vehicle angular speed xcfx89 can be obtained in various manners, such as, for example, by differentiating the phase reference xcex8 (i.e. the phase reference xcex8 currently outputted) generated in the end by the speed electromotive force phase control system according to the present invention, or by converting the vehicle speed measured in some way to the angular speed, and so on.
Secondly, a xcex94xcex8 calculation means 3 calculates a speed electromotive force phase correction amount xcex94xcex8, using a d-axis component Zd and a q-axis component Zq of the estimated speed electromotive force estimated in the speed electromotive force estimation means 2. In general, in the dq rotary coordinate system, the speed electromotive force is induced in either axis d or q theoretically. For example, when coordinate conversion is performed so that the q-axis component of the speed electromotive force may become zero (0), a predetermined direct current voltage is induced in the axis d. However, actually, when the LSM is driven, the speed electromotive force is generated also in the axis of which component is supposed to be zero (0) (i.e. axis q in the above example). When the LSM is controlled in the dq rotary coordinate system, generally the axis component which is supposed to be zero (0) is regulated to be zero (0). It should be noted that in the field dealing with power conversion equipment, transformation of electrical energy, etc., it is general to perform the coordinate conversion and the control so that the q-axis component may become zero (0) in the dq rotary coordinate system.
For instance, when the coordinate conversion is performed so that the q-axis component may become zero (0) as in the above example, the speed electromotive force phase correction amount xcex94xcex8 is calculated by an equation (1) below. Incidentally, by exchanging a denominator and a numerator (i.e. Zd, Zq) in the following equation (1), the coordinate conversion that makes d-axis component become zero (0) can be done.                               Δ          ⁢                      xe2x80x83                    ⁢          θ                =                              tan                          -              1                                ⁢                                    Z              ⁢                              xe2x80x83                            ⁢              q                                      Z              ⁢                              xe2x80x83                            ⁢              d                                                          (        1        )            
Then, a speed electromotive force phase calculation means 4 calculates a speed electromotive force phase xcex8e, by adding the speed electromotive force phase correction amount xcex94xcex8 obtained from the xcex94xcex8 calculation means 3 to the phase reference xcex8 currently outputted.
The speed electromotive force phase xcex8e obtained here by the equation (1) can be used directly as the phase reference xcex8. However, in order to obtain the stable phase reference xcex8 with a minimum deviation even at low speed range when the speed electromotive force is small, a phase signal stabilization means 5 calculates a deviation (phase deviation) between the speed electromotive force phase xcex8e and the phase reference xcex8 currently outputted, and by performing proportional-integral operation of the phase deviation, it outputs the stable phase reference xcex8 with a reduced deviation.
In the present invention, the expression xe2x80x9cunder a predetermined speedxe2x80x9d means a speed range at which the speed electromotive force phase xcex8e cannot be used as the phase reference xcex8 when it is calculated in the conventional manner as shown in FIG. 9, for example. It is because the speed electromotive force becomes too small and the deviation of the speed electromotive force phase xcex8e becomes too large to be ignored. Generally, when the vehicle is running at a speed under 15 km/h, for example, it is difficult to use the conventionally calculated speed electromotive force phase xcex8e as the phase reference.
Specifically, in the speed electromotive force phase control system according to the present invention, the speed electromotive force phase xcex8e is not directly calculated as in the conventional manner shown in FIG. 9, but is obtained by firstly calculating the speed electromotive force phase correction amount xcex94xcex8 from the speed electromotive force in the dq rotary coordinate system and then adding the xcex94xcex8 to the current phase reference xcex8. The computed speed electromotive force phase xcex8e is further processed proportionally and integrally to be made stable, and outputted as a new phase reference xcex8 in the end.
The coordinate conversion to the dq rotary coordinate system herein described includes a coordinate conversion to the dq0 rotary coordinate system in which a zero-phase-sequence component is taken into consideration. For example, when conversion to the dq rotary coordinate system is performed in case that the power conversion means is constituted as a three-phase four-wire system which allows for the zero-phase-sequence component, it is also necessary to consider the zero-phase-sequence component in the dq rotary coordinate system. In this case, the conversion is regarded as a conversion to the dq0 rotary coordinate system. The conversion to the dq rotary coordinate system by the dq conversion means according to the present invention is considered to include the conversion to such dq0 rotary coordinate system. The type of the coordinate system before the coordinate conversion by the dq conversion means is not limited to a three-phase alternating current coordinate system. A two-phase current coordinate system and other coordinate systems are also included.
According to the above speed electromotive force phase control system, the speed electromotive force phase xcex8e is obtained by correcting the phase reference xcex8 with the speed electromotive force phase correction amount xcex94xcex8 obtained from the dq rotary coordinate system, and is outputted further as the phase reference xcex8 through a phase signal stabilization means 5.
Therefore, it is possible to obtain the stable phase reference xcex8 with the minimum deviation even when the vehicle is running at low speed which results in small speed electromotive force. Consequently, the speed electromotive force phase control system according to the invention makes it possible to obtain the stable phase reference xcex8 with the minimum deviation even under the predetermined speed, although it was difficult to obtain the speed electromotive force phase xcex8e when the vehicle is running at a speed under, for example, 15 km/h, as in the case of the conventional manner shown in FIG. 9.
In order to stabilize the speed electromotive force phase xcex8e, the phase reference xcex8 may be calculated in the following manner. Firstly, the phase signal stabilization means 5 performs proportional-integral and double-integral operation of a phase deviation between the speed electromotive force phase xcex8e and the phase reference xcex8 currently outputted, and adds up each computed value (so-called secondary PI control), to calculate the vehicle angular speed xcfx89. Then, the vehicle angular speed xcfx89 is further integrated to obtain the phase reference xcex8.
When the vehicle is running at a fixed speed, a steady-state deviation of the phase reference xcex8 can be reduced by performing proportional-integral operation of the phase deviation and adding up each calculated value (so-called primary PI control). When the vehicle is being accelerated or decelerated, however, the phase reference xcex8 varies showing a quadratic curve and the steady-state deviation cannot be regulated sufficiently by the primary PI control.
By employing the secondary PI control which includes double-integral operation, the steady-state deviation upon accelerating and decelerating the vehicle can be reduced to nearly zero (0). Therefore, according to the above speed electromotive force phase control system, it is possible to obtain the stable phase reference xcex8 with the reduced steady-state deviation.
In the speed electromotive force estimation means 2, for example, the estimated speed electromotive force values Zd and Zq are obtained by performing operation according to the following equation (2).
Z=GIxe2x88x92G∫{AI+BZ+CV}dtxe2x80x83xe2x80x83(2)
where                                           Z            =                          [                                                                    Zd                                                                                        Zq                                                              ]                                ,                      I            =                          [                                                                    Id                                                                                        Iq                                                              ]                                ,                      V            =                          [                                                                    Vd                                                                                        Vq                                                              ]                                ,                      G            =                          [                                                                                          g                      11                                                                                                  g                      12                                                                                                                                  g                      21                                                                                                  g                      22                                                                                  ]                                      ⁢                  
                ⁢                              A            =                          [                                                                                          a                      11                                                                                                  a                      12                                                                                                                                  a                      21                                                                                                  a                      22                                                                                  ]                                ,                      B            =                          [                                                                                          b                      11                                                                                                  b                      12                                                                                                                                  b                      21                                                                                                  b                      22                                                                                  ]                                ,                      C            =                          [                                                                                          c                      11                                                                                                  c                      12                                                                                                                                  c                      21                                                                                                  c                      22                                                                                  ]                                      ⁢                  
                ⁢        and        ⁢                  
                ⁢                                                                              a                  11                                ~                                  a                  22                                                                                                                          b                  11                                ~                                  b                  22                                                                                                                          c                  11                                ~                                  c                  22                                                                        }        :          coefficients set by resistance and inductance of the 
propulsion coil, and the vehicle angular speed ω                   g      11        ~                  g        22            :              gain        ⁢                  xe2x80x83                ⁢        coefficients            
The above equation (2) can be obtained by applying the observer theory in the modern control theory, for example. By setting appropriate values to each component g11-g22 (so-called observer gains) of a matrix G based on the result of experiments and simulations, etc., the estimated speed electromotive force value Z is stably and rapidly calculated, and comes to converge to a true value of the speed electromotive force. Using the estimated speed electromotive force value Z obtained as such makes it possible to obtain the accurate and liable speed electromotive force phase xcex8e.
In the control system of the LSM vehicle, by employing the speed electromotive force phase control system according to the present invention, it is possible to obtain the phase reference xcex8 from the speed electromotive force phase xcex8e, without providing the equipment for detecting the vehicle position on the guideway. It is also acceptable to provide a position detecting phase generation means on the guideway to obtain a position detecting phase xcex8p as a vehicle position signal, and input either of the speed electromotive force phase xcex8e or the position detecting phase xcex8p, selected by an input phase signal selection means, to the phase signal stabilization means 5 as the phase signal.
Specifically, there is an option of selecting either the speed electromotive force phase xcex8e obtained from the speed electromotive force phase calculation means 4 or the position detecting phase xcex8p obtained from the position detecting phase generation means on the guideway.
Such constitution allows the speed electromotive force phase xcex8e to be used as a backup, for example, in case the position detecting phase generation means is out of order, and improves liability of the control system of the LSM vehicle much better.